1. Field of the Invention
The present invention relates to an actuator driving device for driving an actuator using a shape memory alloy.
2. Description of the Background Art
A shape memory alloy (SMA) has a property that it recovers its shape when heated to a temperature equal to or higher than a reverse transformation completion temperature, even if it is plastically deformed when being subjected to an external force at a temperature equal to or lower than a martensite transformation completion temperature. For instance, when the SMA is energized, it generates an exothermic heat by its Joule heat, and when the temperature of the SMA reaches the reverse transformation completion temperature or exceeds the reverse transformation completion temperature, it recovers its shape. The SMA is usable as a material for an actuator, by utilizing the aforementioned property. Concerning the SMA actuator, Japanese Unexamined Patent Publication No. 2000-112526 discloses a driving circuit for driving a movable member which is horizontally movable in a uniaxial direction by an SMA actuator. In using the driving circuit of the SMA actuator, a current to be applied to the SMA actuator is analogly or digitally controlled so as to displace the SMA actuator by an intended amount, whereby the movable object is moved to an intended position in accordance with the applied current.
The conventional art, however, does not disclose an arrangement of reducing the amount of current to be applied to the SMA actuator i.e. an electric power, as compared with an electric power required in a case that the SMA actuator is in a constant driving condition i.e. a temperature or heat equilibrium condition, in other words, an arrangement of suppressing an electric power consumption concerning the SMA actuator. In particular, waste of electric power consumption involves a serious issue in the case where a usable electric power is limited as in the field of a compact portable electric device using a battery or a like device.